The present invention relates to a press die that is used to form, for example, a separator for a fuel cell.
For a typical separator used in a fuel cell, a configuration is known in which passages for hydrogen and oxygen are formed by protrusions and recesses, which are formed in a workpiece plate made of hard material such as titanium.
Japanese Laid-Open Patent Publication No. 2014-231073 discloses a press die apparatus that has a press die for forming one such separator. The press die apparatus includes a lower die and an upper die. The lower die has a shaping face with protrusions and recesses on its upper surface. The upper die is arranged above the lower die in an approachable-separable manner with respect to the lower die. The upper die has, on its lower surface, a shaping face with protrusions and recesses corresponding to the shaping face with protrusions and recesses of the lower die. With a workpiece plate mounted on the shaping face of the lower die, the upper die is moved closer toward the lower die to press the workpiece plate to form protrusions and recesses on the workpiece plate between the shaping faces of the two dies.
In the conventional press die apparatus disclosed in the aforementioned publication, the upper and lower dies are each configured by die members each having a quadrangular prism-like shape. In each of the dies, the die members are received and aligned in a frame arranged on a table.
Wedge units are arranged between each frame and the corresponding die members. Each of the wedge units includes a first wedge member and a second wedge member. The first wedge member is in contact with the die members and is in a floating state. The second wedge member is in contact with the first wedge member at an inclined surface, is also in contact with the frame, and is fixed to the table by means of screws. The inclined surfaces of the two wedge members are pressed against each other to produce a wedge effect by which the die members are pressed by the first wedge member in an aligned state and are thus fixed in the aligned state.
However, in the conventional press die apparatus, after repeating pressing many times, vibration and impact caused by the pressing gradually move each first wedge member, which is in a floating state, toward the workpiece plate against the wedge effect. The first wedge member may thus come into contact with the workpiece plate. This causes adverse influence on the forming accuracy of the workpiece plate.
To prevent this problem, the angles of the inclined surfaces of the two wedge members may be increased. However, this increases the force by which the inclined surfaces of the wedge members are pressed against each other. This correspondingly increases the force component that acts on each frame, which is located on the outer side of the corresponding wedge unit, thus deforming the frame. Also, great force may act on the screw, with which the second wedge member is fixed, in a curving direction or axial direction, thus deforming the screw or displacing the second wedge member together with the screw from a predetermined position. Further, if the first wedge member moves in a state in which the inclined surfaces of the two wedge members are pressed against each other, the inclined surfaces may be damaged. These problems can deteriorate the machining accuracy for the workpiece plate.